In certain disease states, a derangement of cellular metabolism can affect the level of expression of one or more DAMs. In some circumstances, this cellular derangement may lead to a change in the levels of expression of the DAM. Thus, each disease causing agent or disease state may have associated with it a DAM which may be crucial in the immune recognition and/or the elimination and/or control of a disease causing agent or disease state in a host organism. In this way, the DAM may be capable of acting as a marker not only for the diagnosis of disease states but also for the accurate staging of the disease profile so that the appropriate therapy may be designed.
A particular example of DAMs which have been well characterised include the tumour-associated antigens (TAAs). A number of oncofoetal or tumour-associated antigens (TAAs) have been identified and characterised in human and animal tumours.
These TAAs include carcinoembryonic antigen (CEA), TAG72, c-erB2, (underglycosylated) MUC-1 and p53, epithelial glycoprotein-2 antigen (EGP-2; also known as EGP40, Ep-CAM, KSA, C017-1A or GA733-2) and the 5T4 antigen. In general, TAAs are antigens which are expressed during foetal development but which are downregulated in adult cells, and are thus normally absent or present only at very low levels in adults. However, during tumourigenesis, tumour cells have been observed to resume expression of TAAs. Thus, it is thought that malignant cells may be distinguished from their non-malignant counterparts by resumption of expression of TAAs. Consequently, application of TAAs for (i) in vitro and/or in vivo/ex vivo diagnosis of tumour disorders; (ii) for imaging and/or immunotherapy of cancer has been suggested and (iii) as indicators of progression of tumour associated disease;
In order to mount a humoral and/or cellular immune response against a particular disease, the host immune system must come in contact with a DAM. In addition to recognising foreign antigens, T cells often need additional stimulation to become fully activated. It is now becoming apparent that two signals are required for activation of naive T-cells by antigen bearing target cells. One signal is an antigen specific signal, delivered through the T-cell receptor and the second signal is an antigen independent or co-stimulatory signal leading to lymphokine products. These additional signals are delivered through other receptors (such as CD28 and CD40L) on the T cell that interact with ligands (such as B7 and CD40) which are present on professional antigen presenting cells (APCs), such as dendritic cells and macrophages, but which are absent from other cells. These co-stimulatory ligands are often referred to as co-stimulatory molecules.
By way of example, the B7 family (namely B7.1, B7.2, and possibly B7.3) represent a recently discovered, but important group of co-stimulatory molecules. B7.1 and B7.2 are both member of the Ig gene superfamily. If a T lymphocyte encounters an antigen alone, without co-stimulation by B7, it will respond with either anergy, or apoptosis (programmed cell death). If the co-stimulatory signal is provided it will respond with clonal expansion against the target antigen. No significant amplification of the immune response against a given antigen is thought to occur without co-stimulation (June et al (Immunology Today 15:321-331, 1994); Chen et al(Immunology Today 14:483-486); Townsend et al (Science 259:368-370)). Freeman et al(J. Immunol. 143:2714-2722, 1989). Azuma et al(Nature 366:76-79, 1993). Thus, it has been postulated that one method for stimulating immune recognition of diseased cells which are poorly immunogenic would be to enhance antigen presentation and co-stimulation of lymphocytes in the presence of the DAM.
By way of example, it has been shown that disease states such as cancer, established tumours may be poorly immunogenic despite the fact that they commonly express DAMs. Transfection of the genes encoding B7-1 and B7-2, either alone or in combination with cytokines, have been shown to enhance the development of immunity to experimental tumours in animal models (e.g. Leong et al. 1997 Int. J. Cancer 71: 476-482; Zitvogel et al. 1996 Eur. J. Immunol. 26:1335-1341; Cayeux et al. 1997 J. Immunol 158:2834-2841). However, in translating these results into a practical treatment for human cancer, there are a number of significant problems to be overcome. A major problem in such studies has been the need to deliver B7 genes in vivo to a large number of cells of the tumour to achieve efficacy. A second problem has been the selective target expression of B7 to the tumour cells to avoid inappropriate immune cell activation directed against other cell types. Some solutions to these problems have been addressed in WO 98/55607 where a tumour interacting protein (TIP) such as a tumour binding protein (TBP) has been used to selectively target a co-stimulatory molecule to tumour cells.
Recombinant DNA technologies have been applied to develop antibodies that recognise DAMs (Hoogenboom et al 1998 Immunotechnology 4: 1-20; and Winter 1998 FEBS Lett 458: 92-94. Recently, there has been considerable interest in using antibody gene libraries to generating antibodies, such as a single chain antibody (ScFv Abs). It is well known that in certain circumstances, there are advantages of using ScFv Abs, rather than whole antibodies. The smaller size of the fragments allows for rapid clearance, and may lead to improved tumour to non-tumour ratios. However, many efforts have failed to produce ScFv Abs of high specificity. Moreover, whole IgGs are regarded as a better format for therapeutic Mabs than ScFc Abs as they are regarded as having an extended serum half life (see Vaughan et al 1998, Nature Biotech 16: 535-539).
The present invention seeks to provide an ScFv Ab raised against a DAM which is useful in the treatment of disease conditions associated with a DAM.